Orth et al. disclose in U.S. Pat. No. 6,907,790 B2 such a method for determining relative pressure, in the case of which a first absolute pressure measuring device measures a process pressure and a second absolute pressure measuring device measures an atmospheric pressure. The atmospheric pressure registered by the second measuring device is transmitted to the first measuring device, whereupon the first measuring device calculates the relative pressure. The atmospheric pressure can, in such case, be transmitted especially using the HART-multidrop method. For fill-level measurements, which, in the case of Orth et al., are clearly the main interest, it is, as a rule, not absolutely required that a measured value of the atmospheric pressure be obtained simultaneously with a measured value of the process pressure, since the atmospheric pressure usually changes only slowly. In case, however, processes with more dynamic parameters are to be monitor, deviations between the points in time of the registering of the different auxiliary measured variables, which enter into the determining of the measured variable, can cause considerable corruption of the measured variable to be determined.